1. Field of the Invention
This invention relates to methods and apparatus for preheating particulate feed material for a rotary kiln with hot exit gases from the kiln, such as for the production of cement, and in particular, to the balanced feeding of raw materials to a first stage of preheating in a pair of cyclone type gas-to-solids heat exchangers.
2. Description of the Prior Art
Preheaters for kilns are known to the prior art that involve preheating finely divided raw materials suspended in and moving generally counter to the flow of heated kiln exit gases, and in which at least the first stage of preheating takes place in a pair of parallel devices such as cyclone dust-gas separators. Examples of such preheaters are disclosed in U.S. Pat. No. 2,663,560 of Dec. 22, 1953; U.S. Pat. No. 2,733,909 of Feb. 7, 1956; U.S. Pat. No. 2,785,886 of Mar. 19, 1957; U.S. Pat. No. 2,797,077 of June 25, 1957; U.S. Pat. No. 3,083,472 of Apr. 2, 1963; U.S. Pat. No. 3,102,719 of Sept. 3, 1963; U.S. Pat. No. 3,259,997 of July 12, 1966; and U.S. Pat. No. 3,288,450 of Nov. 29, 1966. Each of those patents discloses apparatus and operations in which raw material is fed from above the preheater, downwardly through a vertical pipe, into the center of a rising gas stream which divides and carries the material into a pair of parallel arranged cyclone type solids-gas separator heat exchangers. None of these patents disclose any means for adjusting the flow of material into the two parallel first stage preheating devices.
Sometimes, however, an arrangement of a plant is such that it is not convenient or desirable to feed the preheater from above. Raw material may then be fed to the outer periphery of a rising gas stream as shown in U.S. Pat. No. 3,726,045 of Apr. 10, 1973 and U.S. Pat. No. 3,752,455 of Aug. 14, 1973. This latter patent discloses an apparatus in which such peripheral fed material is carried in an upwardly moving gas stream and divided between a pair of parallelly arranged first stage preheating devices, without any way to adjust the distribution of feed material, and it has been our experience that such an apparatus is much more likely to operate with an unbalanced flow of material between the two devices of first stage preheating.
It is to this problem of an unbalanced distribution of raw material to a pair of first stage preheating heat exchangers that the present invention is directed, and to solve this problem is this invention's object.